1. Field of the Invention
The present invention relates to an AT ISG vehicle equipped with an ISG (Idle Stop and Go) device, and particularly, to an engine restart control method that improves operability of restarting by reducing engine torque when an engine is restarted from an idle-stop state.
2. Description of Related Art
Recently, technologies for improving fuel efficiency to reduce CO2 have been developed in various ways.
The ISG system is a device that stops the engine when a vehicle stops and automatically starts the engine when the vehicle starts.
The ISG device allows normal traveling by automatically idle-stopping the engine under predetermined conditions while receiving information, such as the speed of the vehicle, the revolution speed of the engine, and the temperature of the cooling water, and then automatically restarting (Go) the engine when restart is required by the driver's intention and the conditions of the vehicle itself.
The condition for entering the idle-stop in the ISO device is a state with the engine sufficiently warmed up, that is, a stop state where the vehicle speed is not detected and the transmission is at the neutral stage with the cooling water maintained at a predetermined temperature or more, and when a predetermined time passes after the brake pedal is operated, the engine is stopped to increase fuel efficiency and stabilize emission. It is possible to achieve an effect of an increase in fuel efficiency of about 5 to 15% by applying the ISO device.
In general, in order to apply the ISG device to an AT vehicle, it is necessary to additionally provide an electric sub-oil pump that supplies oil to the transmission with the engine idle-stopped, which cost competitiveness of inexpensive vehicles. Accordingly, an AT ISG system without a sub-oil pump has been developed.
FIG. 1 is an operational flowchart showing a control method of a common AT ISG vehicle.
An engine is stopped (S12) when an engine stop condition set in advance in a vehicle is satisfied while the vehicle travels (S11). Thereafter, when an engine restart condition set in advance in the vehicle is satisfied (S13), a starter motor is operated (S14) such that the engine is restarted and the vehicle is started (S15).
FIG. 2 is a graph showing clutch slip generated in restarting of the engine of an AT ISG vehicle without a sub-oil pump.
In the AT ISG vehicle without a sub-oil pump, since oil is not supplied into the transmission in the idle-stop state, the low oil pressure is exerted in the transmission. In this state, when shifting is attempt by starting (accelerating) of the vehicle after the engine is restarted, clutch slip is generated and a large temporary shock is generated to suddenly assist the oil pressure in the transmission until the oil pressure in the transmission becomes a predetermined level due to the low oil pressure. Further, the clutch of the transmission is damaged by repetitive clutch slip and operability is deteriorated by the shock of the transmission.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.